Amide-Directed Catalytic Asymmetric Hydroboration of Trisubstituted Alkenes
作者:Sean M. Smith、James M. Takacs
DOI:10.1021/ja908257x
日期:2010.2.17
rhodium-catalyzed reaction is stereospecific. In addition, simple TADDOL-derived phenyl monophosphite ligands in combination with Rh(nbd)(2)BF(4) afford highly enantioselective catalysts (seven examples, 91-98% ee). These catalysts provide an alternative methodology to prepare Felkin or anti-Felkin acetate-aldol products and related derivatives that are obtainable from the intermediate chiral organoboranes
Regioselective nucleophilic ring opening of epoxides and aziridines derived from homoallylic alcohols
作者:David Tanner、Thomas Groth
DOI:10.1016/s0040-4020(97)10053-9
日期:1997.11
of the nucleophile to C-3 via a six-membered transition state, leading to 1,4-diols or 1,4-amino alcoholderivatives. In general, the epoxy alcohols gave poorer regioselectivity than the N-tosyl aziridino alcohols, for which selectivities of >95:5 were routinely obtained. The activating effect of a phenyl group at C-4 led to a switch in regiochemistry, with the 1,3-diol or 1,3-amino alcohol derivative
A new strategy to construct a CC–CF3 subunit via CuBr-catalyzed domino reaction of homopropargyl amines: an efficient synthesis of trifluoromethyl containing building blocks 4-trifluoromethyl-2,3-dihydro-pyrroliums
A new strategy for the construction of a CCâCF3 subunit has been developed via CuBr-catalyzed domino cyclizationâtrifluoromethylation of homopropargyl amines with Umemoto's reagent. 4-Trifluoromethyl-2,3-dihydro-pyrroliums were produced in high yields. The usefulness of these products has been demonstrated by the transformation of them into various other trifluoromethylated molecules.
A novel formal [4 + 1]-cycloaddition of readily available homopropargyl alcohols with diazo dicarbonyl compounds is described, which involves tandem O-H insertion/Conia-ene cyclization under cooperative Rh(II)/Zn(II) catalysis. This reaction provides easy access to various substituted tetrahydrofurans and exhibits complete E-selectivity in the case of nonterminal alkynes.
Sequential Cyclization/Silylation of Dienynes Catalyzed by an Organoyttrium Complex
作者:Gary A. Molander、William H. Retsch
DOI:10.1021/jo980521t
日期:1998.8.1
The organoyttrium complex Cp*2YCH3. THF (Cp* = C5Me5) has been shown to be an effective precatalyst for the selective sequential cyclization/silylation of dienynes. The catalyst's ability to insert the alkyne in preference to the alkenes in a regioselective manner, combined with the high diastereoselectivity of the intramolecular insertion process, leads to bicyclo[3.3.0]octane products in high yield. The stereochemistry of the exocyclic olefin, the ring fusion, and the ring substituents are all controlled in the reaction. The cyclization of dienynes thus affords silylated carbobicyclics with high diastereoselectivities in excellent yields.